An adult human contains about 5 liters of blood, which includes valuable components such as red blood cells, liquid blood plasma and platelets. In view of the substantial therapeutic and monetary value of these blood components, a variety of techniques have been developed to separate blood into its component fractions while ensuring maximum purity and recovery of each of the components. Additionally, since blood and blood components may include varying numbers of white blood cells (leukocytes), which may cause undesirable effects when administered to a patient, blood processing techniques may also include leukocyte depleting the blood or blood components, e.g., by passing the blood or blood components through a leukocyte depletion device.
In some techniques for blood processing, a container such as a flexible bag is connected to a blood donor, and filled with a unit of whole blood. The container is disconnected from the donor, and the blood is further processed to provide the desired separated component(s). Alternatively, in some other techniques, e.g., apheresis, the donor may remain connected to a blood processing system during component separation, while the remainder of the blood, depleted of the desired component, is returned to the donor. Blood may be passed transversely across a membrane, e.g., a planar sheet or a bundle of hollow fibers, to separate the component from the blood. Typically, centrifugation is employed to separate the component from the blood. The separated component may be returned to the donor, or collected for a later use, such as a transfusion.
There are a variety of apheresis procedures, which may be generally classified according to the particular component to be separated and/or the method of separation. For example, the separation of platelets during apheresis is known as plateletpheresis or thrombocytapheresis, the separation of young red blood cells is known as neocytapheresis, and the separation of plasma is known as plasmapheresis.
With respect to classification by the mode of separation, among those procedures are methods including continuous flow, and intermittent flow. Typically, during continuous flow, blood is withdrawn from a donor from one venipuncture site using a pump, processed to separate at least one desired component, and the component depleted blood is returned to the donor through a second venipuncture site, essentially simultaneously, using an additional pump.
Typically, during intermittent flow, which utilizes a single venipuncture site, blood is withdrawn from an individual using a pump, and the blood is processed to separate at least one component. The pump is then reversed to return the component depleted blood to the donor. These cycles of withdrawal and return may be repeated as necessary until the desired amount of separated component is obtained. For example, during intermittent flow plateletpheresis, there may be several cycles of withdrawal of blood from the donor and separation of platelet-containing fluid from the blood, followed by return of the platelet-depleted red cell-containing blood, to the donor, to obtain a therapeutic dose of platelets.
Continuous flow and intermittent flow apheresis protocols may include centrifugation, and those techniques including centrifugation are typically referred to as continuous flow centrifugation (CFC), and intermittent flow centrifugation (IFC), respectively. Typically, during these protocols, blood may be spun in a centrifuge bowl and/or exposed to a rotating membrane to separate the desired component(s).
There are a number of drawbacks associated with apheresis systems, particularly with respect to processing the separated component. For example, during continuous flow and intermittent flow plateletpheresis, since a limited volume of blood may be withdrawn from the donor at any given time, some methods include accumulating or pooling the separated platelets until almost the entire procedure, i.e., the separation of the desired amount of platelets, is complete. The apheresis system is then disconnected from the donor, and the accumulated platelets may be leukocyte depleted, e.g., by passage through a leukocyte depletion device. This is a time consuming, inefficient process, in that extra time is required to leukocyte deplete the large quantity of accumulated platelets after plateletpheresis is completed. Similar drawbacks are associated with other apheresis protocols, e.g., involving accumulating and leukocyte depleting other components, such as red cells and/or plasma.
Among other disadvantages, the leukocyte depletion of the accumulated component, e.g., platelets, requires the use of a correspondingly larger leukocyte depletion device to obtain a desired leukocyte depletion efficiency in an acceptable amount of time. Furthermore, due to its larger size, the device may hold up an increased amount of valuable platelets which may be difficult to recover in a cost effective manner.
Additionally, the presence of air or gas, for example, in a container with the separated component, in the fluid flow path of the separated component and/or in the component fluid itself, may adversely affect processing efficiency and/or impair the quality of the component and may decrease its storage life. For example, since the platelet containing fluid may displace gas as it passes from one location to another, it may be difficult and/or time consuming to efficiently pass the fluid through a porous medium such as a leukocyte depletion medium, since the displaced gas may block the medium. Similarly, since the platelet containing fluid may be "foamy," i.e., include air bubbles, the presence of air may present difficulties when the fluid is to be passed through a porous medium such as a leukocyte depletion medium. Moreover, oxygen may be associated with an increased metabolic rate (during glycolysis), which may lead to decreased storage life and decreased viability and function of blood components such as red cells and/or platelets. Thus, it may be desirable to minimize the presence of air when blood components are being processed and/or before the blood components are stored, particularly when they are to be stored for long periods of time, e.g., several days or more.
Accordingly, there is an unaddressed need in the art for providing leukocyte depletion during apheresis, thereby decreasing the time needed to separate and leukocyte deplete a blood component. There is also a need for a system that provides for minimizing the presence of air while processing the separated component, e.g., while passing the separated component through a porous medium, and/or for minimizing the presence of air before storing the separated component.
Moreover, there is a particular need for a system that is compatible with existing systems, including automated systems, and provides for separation of a component of blood, separation of air from the component flow path, and leukocyte depletion of the component, preferably without extending the time that the donor is attached to the processing system.
These and other advantages of the present invention will be apparent from the description as set forth below.